Taken from https://stackoverflow.com/questions/12641676/how-to-get-a-status-of-a-running-query-in-postgresql-database, https://stackoverflow.com/questions/35319597/how-to-stop-kill-a-query-in-postgresql

postgresql_util.sql

--active query list
SELECT datname, pid, state, query, age(clock_timestamp(), query_start) AS age 
FROM pg_stat_activity
WHERE state <> 'idle' 
    AND query NOT LIKE '% FROM pg_stat_activity %' 
ORDER BY age;

--shutdown
SELECT pg_cancel_backend(<pid of the process>); 

--kill
SELECT pg_terminate_backend(<pid of the process>); 

--total relation size
SELECT pg_size_pretty(pg_total_relation_size('relation_name')); 

--relation size
SELECT pg_size_pretty(pg_relation_size('relation_name'));